N,M=map(int,input().split())
dp=[0]*(M+1)
np=[0]*(M+1)
L=[]
for i in range(N):
  c,d=map(int,input().split())
  L.append((c,d))
L.sort()
result=0
for i in range(N):
  a,b=L[i][:]
  for x in range(a,M+1):
    np[x]=max(dp[x-a]+b,np[x])
  for x in range(a):
    np[x]=dp[x]
  w=max(np)
  result=max(result,w)
  for x in range(M+1):
    if 2*x>M:
      break
    dp[2*x]=np[x]
print(result)